The present invention relates to a color cathode ray tube, and in particular to a cathode ray tube capable of improving withstand voltage characteristics and displaying high-resolution color images by ensuring of high precision of dimensions and shapes of cup-shaped electrodes among a plurality of electrodes of an electron gun housed in its vacuum envelope.
Color cathode ray tubes such as a color picture tube and a display tube, which are typical cathode ray tubes, are widely used for reception of TV broadcast and monitors of various kinds of information processing equipment because of their high-definition image reproduction capability.
Color cathode ray tubes of such a kind have a vacuum envelope comprised of a panel, a neck and a funnel for connecting the panel and the neck, a phosphor screen formed on an inner surface of the panel, and an electron gun housed in the neck for projecting electron beams toward the phosphor screen. Especially, widely used are color cathode ray tubes employing an in-line type electron gun for projecting a plurality of electron beams parallel with each other in a horizontal plane.
FIG. 5 is a side view of an essential part of an embodiment of a configuration of an in-line type electron gun used for a color cathode ray tube, viewed in a direction perpendicular to a direction of the in-line arrangement of the electron beams.
In FIG. 5, reference numeral 31 denotes cathodes, 32 is a first electrode serving as a control electrode, 33 is a second electrode serving as an accelerating electrode, and the cathodes 31, the first electrode 32 and the second electrode 33 form an electron beam generating section. Reference numeral 34 denotes a third electrode, and 35 is a fourth electrode.
In this example, the fourth electrode 35 is formed of two cup-shaped electrodes 35a and 35b, and they serve as two focus electrodes. Reference numeral 36 denotes a fifth electrode, and the fifth electrode 36 and the cup-shaped electrode 35b of the fourth electrode 35 form a main lens therebetween. Reference numeral 37 denotes a shield cup, which is welded to the fifth electrode 36. The cathodes 31 and the first to fifth electrodes 32-36 are spaced with predetermined spacings and fixed in the predetermined order by a pair of insulator support rods (multiform glasses) 38.
Reference numeral 39 denotes a stem, and the cathodes and the electrodes are supplied with display signals or operating voltages via stem pins 40 sealed through the stem 39. Three electron beams are generated by the electron beam generating section which is a triode section comprised of the cathodes 31, the first electrode 32 and the second electrode 33, and are accelerated and focused by the third electrode 34, the fourth electrode 35 and the fifth electrode 36 such that the three electron beams are subjected to a desired focusing action by the main lens formed between opposing end faces of the fifth electrode 36 and the electrode 35b of the fourth electrode 35 and then directed toward the phosphor screen.
In this type of an electron gun, the first electrode 32 and the second electrode 33 are plate-like electrodes, and the third electrode 34, the fourth electrode 35 and the fifth electrode 36 are cup-shaped single-electrodes, respectively, or compound electrodes fabricated by welding together plural electrode members including a cup-shaped electrode member and a plate-like member, respectively.
FIGS. 6A to 6C are illustrations for explaining details of the fifth electrode 36 which is one of cup-shaped electrodes used in the electron gun of FIG. 5, FIG. 6A is a plan view of the fifth electrode 36, FIG. 6B is a front view thereof, and FIG. 6C is a cross-sectional view of the fifth electrode 36 taken along line VICxe2x80x94VIC of FIG. 6A.
As shown in FIGS. 6A to 6C, the cup-shaped fifth electrode 36 has a generally rectangular flange 36f and a tubular portion 36b rising approximately perpendicularly and continuously from the flange 36f. The tubular portion 36b has an approximately oval opening in a cross section perpendicular to an axis 36c of the tubular portion 36b, that is, an approximately oval opening of the shape having two arcs 36b1 at both ends thereof and two straight lines 36b2 at the central portions joining the two arcs 36b1. The three electron beams pass through the approximately oval opening. Reference numeral 36d denotes a turned-up portion, which is turned up inwardly from a top surface 36e of the tubular portion 36b to extend toward the flange 36f. In some cup-shaped electrodes, the turned-up portion 36d is omitted.
The flange 36f comprises arc-shaped flange portions 36f1 and straight flange portions 36f2 which are formed outside of the tubular portions 36b. A structure of such a cup-shaped electrode is disclosed in Japanese Patent Application Laid-open No. Sho 55-74036 (laid-open on Jun. 4, 1980), for example.
Generally, such cup-shaped electrodes are fabricated by punching out sheets of desired dimensions from a long strip of a material, and then performing various operations such as the drawing of the sheets, heat treatment, and putting the drawn parts in final shape.
In the above prior art cup-shaped electrode, there has been a problem in that defects such as defective outside dimensions occur in the flange 36f after the drawing process, as indicated by broken lines 61, 62 in FIGS. 6A and 6B.
As described above, such cup-shaped electrodes are fabricated by the process steps including the drawing process steps. The tubular portion 36b has an approximately oval cross section in a plane perpendicular to the axis 36c of the tubular portion 36b, and consequently, in the drawing process step in which the tubular portion 36b is formed to rise from the flange 36f, the arc-shaped portions 36w1 of the tubular portion 36b are subjected to drawing action, but the straight portions 36w2 of the tubular portion 36b are subjected to bending, action, that is to say, the work piece is subjected to different forming actions depending upon the positions of the work piece in the same processing step. As a result, the arc-shaped portions 36w1 and the straight portions 36w2 differ from each other in the amount of excess material capable of flowing elsewhere, and consequently, the thickness of the arc-shaped flange portions 36f1 becomes greater than that of the straight flange portions 36f2.
The parts as drawn are subjected to heat treatment, and then are press-forming the whole parts including the flange 36f into final shape by using a die. If the parts of the above-mentioned shape were intended to be press-formed into final shape, it was difficult to ensure the flatness of the flange 36f and the parallelism of the flange 36f with the top surface 36e, and further the tubular portion 36b tilted with respect to the normal to the flange 36f, and as a result, the desired shapes and dimensions of the electrodes were not obtained, and further desired interelectrode spacings and concentricity between electron beam apertures which are important factors in withstand voltage and resolution characteristics could not be obtained in assembling the electron gun, and consequently adverse effects were caused to characteristics of the color cathode ray tube.
As measures to solve such various problems, there is a special technique to press-form the thick arc-shaped flange portions 36f1 by pressing the flange portions 36f1 against the shaping die strongly, but it complicates the processing steps and also the arc-shaped flange portions 36f1 expand locally and outwardly as indicated by broken lines 62 in FIG. 6A, and edges of the arc-shaped flange portions 36f1 become pointed in a longitudinal cross section and cause a problem in withstand voltage characteristics.
On the other hand, to prevent the above-mentioned local and outward expansions of the arc-shaped flange portions 36f1, it is necessary to reduce pressures in forming by using a die, but, in this case, there is a possibility that press-forming becomes insufficient. By this measure, it is difficult to ensure the flatness of the flange 36f and the parallelism of the flange 36f with the top surface 36e, and eliminate the tilt of the tubular portion 36b from the normal to the flange 36f, and as a result, there have been various problems to be solved in that adverse effects were caused to characteristics of the color cathode ray tube.
It is an object of the present invention to solve the above-mentioned various problems with the above prior art and provide a color cathode ray tube provided with an electron gun employing a highly reliable electrode capable of forming the tubular portion perpendicularly to the flange, suppressing changes in outside dimensions of the flange, and ensuring the parallelism between the flange and the top surface of the tubular portion with high precision.
To achieve the above object, in accordance with an embodiment of the present invention, there is provided a color cathode ray tube comprising a vacuum envelope including a panel portion, a neck portion and a funnel portion for connecting the panel portion and the neck portion, a phosphor screen formed on an inner surface of the panel portion, and an electron gun housed in the neck portion, the electron gun comprising an electron beam generating section having a cathode, an electron beam control electrode and an accelerating electrode arranged in the order named for emitting three in-line electron beams toward the phosphor screen, and an electron beam focusing section for focusing the three in-line electron beams from the electron beam generating section onto the phosphor screen, the electron beam generating section and the electron beam focusing section being mounted in predetermined spaced relationship on a plurality of insulator support rods, the electron beam focusing section including at least one cup-shaped electrode having a tubular portion and a flange formed continuously from the tubular portion, the tubular portion having a generally rectangular cross section having an outwardly curved portion at each side thereof in a direction of arrangement of the three in-line electron beams in a plane perpendicular to an axis of the color cathode ray tube, the flange having a generally rectangular cross section having an outwardly curved portion at each side thereof in the direction of arrangement of the three in-line electron beams in the plane perpendicular to the axis of the color cathode ray tube, and the flange being formed with a locally thinned-down portion.
In the above configuration, uniform pressures are applied to the whole work piece in press-forming, therefore a cup-shaped electrode with high precision in dimensions and shapes thereof is obtained, and consequently, it is possible to provide a color cathode ray tube superior in characteristics such as withstand voltage characteristics by using this superior cup-shaped electrode.
The present invention is not limited to the above configuration, but various changes and modifications can be made to the above configurations without departing from the nature and spirit of the present invention.